Our objective is a better understanding of mammalian reproduction. This we hope to accomplish by the study of fertilization in vitro of mouse ova by epididymal sperm. The resulting zygotes will be subjected to microsurgery to remove the female pronucleus. From the residues we hope to develop haploid cell lines for studies in mutagenesis. We will also study spontaneous parthenotes which occur in LT/Sv mice by making chimeras with normal embryos to salvage the germ cell line of the parthenote. We will look for twins and spontaneous chimeras in LXBJ/Sv mice which produce some twin ova rather than an ovum or a second polar body. We will continue our studies on hermaphrodites, sex ratio, sex pheromones, and granulosa cell tumors of young SWR/J mice. We will investigate some of the many interesting reproductive phenomena which arise in the extensive mouse colonies of the Jackson Laboratory.